JavaScript和TypeScript范围问题

Question

我正在尝试使用typescript，Knockout和azure移动服务来获取一些数据。 问题是当我从azure获取数据时，它是异步的，我无法再获取viewmodel对象。 我认为这是一些范围/关闭问题，请帮我找到解决方案。 在Done（）的回调函数中它为null;

这是我的TypeScript代码：

class pmViewModel {
    public welcomeMsg: string;
    public totalCount: number;
    constructor () {
        this.welcomeMsg = "";
    }
}

class Manager {
    client: any;
    portalVM: pmViewModel;
    constructor () {
        this.client = new WindowsAzure.MobileServiceClient("url", "key");
        this.portalVM = new pmViewModel();
    }

    LoadData() {
        console.log("load data for management portal");
        this.portalVM.welcomeMsg = "Hello";
        this.portalVM.totalCount = 0;
        var dataTable = this.client.getTable('dataTable');

        dataTable.take(1).includeTotalCount().read().done(this.populateTotal,this.portalVM);

        ko.applyBindings(this.portalVM);
        };

        populateTotal(result, vm) {
            console.log(result);
            console.log(vm); //null here
            this.portalVM.totalCount = 100000;////this is also null
        }
}

并生成JavaScript代码：

var pmViewModel = (function () {
    function pmViewModel() {
        this.welcomeMsg = "";
    }
    return pmViewModel;
})();
var Manager = (function () {
    function Manager() {
        this.client = new WindowsAzure.MobileServiceClient("url", "key");
        this.portalVM = new pmViewModel();
    }
    Manager.prototype.LoadData = function () {
        console.log("load data for management portal");
        this.portalVM.welcomeMsg = "Hello";
        this.portalVM.totalCount = 0;
        var dataTable = this.client.getTable('dataTable');
        dataTable.take(1).includeTotalCount().read().done(this.populateTotal, this.portalVM);
        ko.applyBindings(this.portalVM);
    };
    Manager.prototype.populateTotal = function (result, vm) {
        console.log(result);
        console.log(vm);
        this.portalVM.totalCount = 100000;
    };
    return Manager;
})();

Answer 1

这里的相关行：

dataTable.take(1).includeTotalCount().read().done(this.populateTotal,this.portalVM);

你需要捕获populateTotal的'this'绑定，因为它将被调用为没有上下文的回调。

选项1：

[etc...].done((result, vm) => this.populateTotal(result, vm), this.portalVM);

选项2：

[etc...].done(this.populateTotal.bind(this), this.portalVM);